1. Field of the Invention
The present invention relates to a conduction device for ensuring the conduction between a first member and a second member.
2. Description of Related Art
Conventionally, there are known shield cases for receiving electronic devices having electronic circuit boards and electronic circuits or the like (for example, refer to reference 1: Japanese Unexamined Patent Application Publication No. 6-283871, page 3, and reference 2: Japanese Unexamined Patent Application Publication No. 10-200283, page 3).
A shield case according to the reference 1 is formed of a metal material in a substantially box-like shape with the upper face formed with an opening. The side plate portion of the shield case is cut-back toward the inside of the shield case, and a cut-back portion for placing periphery portion of four corners of the electronic circuit board is formed in a substantially rectangular shape. In the central area of the cut-back portion, a screw hole to be screwed with a setscrew is bored. In the peripheral vicinity of the screw hole, a plurality of projections is formed in a radial pattern so as to protrude from the upper face of the cut-back portion. On the other hand, in the periphery of the four corners of the electronic circuit board, an insertion hole to be inserted with a setscrew is bored respectively. In the peripheral vicinity of the insertion hole in the bottom face of the electronic circuit board, earth pattern, which is connected to the grounding of the electronic circuit and has a radial pattern corresponding to the projections of the shield case, is formed.
When an electronic circuit board is attached to the shield case, a mound of the solder is formed by applying solder to the earth pattern of the electronic circuit board, and then, the electronic circuit board is placed on the cut-back portion of the shield case. After that, by screwing a setscrew into the screw hole in the shield case via the insertion hole in the electronic circuit board, the projections of the cut-back portion of the shield case are allowed to cut into the mound of the solder on the electronic circuit board. Thereby, the conduction between the electronic circuit and the shield case is ensured as well as the electronic circuit board is assembled to the shield case.
A shield case according to the reference 2 is formed of a metal material in a substantially box-like shape, and comprises a first case of a substantially box-like shape with one face formed with an opening and a second case of a substantially rectangular shape with another face formed with an opening. In a side plate portion of the first case, an insertion hole to be inserted with a setscrew is bored. In the peripheral vicinity of the insertion hole, a sharp catch, which is cut back so as to protrude toward the inside of the first case, is formed. In a side plate portion of the second case, a screw hole to be screwed with a setscrew is bored.
When receiving an electronic circuit board in the shield case, for example, after placing the electronic circuit board inside the space of the second case, the inner surface of the side plate portion of the first case and the outer surface of the side plate portion of the second case are engaged so as to overlap with each other. After that, by screwing a setscrew into the screw hole in the second case via the insertion hole of the first case, the sharp catch of the first case is allowed to cut into a metal face constituting the second case. Thus, the conduction between the first case and the second case is ensured as well as the first case is fixed to the second case.
However, in the structure according to the reference 1, such a structure that projections of the shield case are allowed to cut into the mound formed on the earth pattern of the electronic circuit board using the setscrew, is adopted. Accordingly, there is a possibility that the cut-in amount of the projections might change depending on the magnitude of the torque of the screwed setscrew or the hardness of the surface of the projections. Therefore, there arises such a problem that the contact resistance between the mound and the projections might change.
Also, in the structure according to the reference 2, same as the structure according to the reference 1, such a structure that the sharp catch on the first case is allowed to cut into the metal surface of the second case using the setscrew, is adopted. Due to the same reason as the structure according to the reference 1, there arises such a problem that the contact resistance between first case and the second case might change.